1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting element and a method for fabricating the same.
2. Description of the Related Art
Generally, an optical element and an electrical element based on a nitride semiconductor have been variously developed until now. Application of the nitride semiconductor becomes broad in various fields. Actually, a light-emitting diode and a laser diode based on the nitride semiconductor are used in a display, such as a colored electric sign and a signal lamp, and in a pickup device of an optical recording medium with high density.
Such a nitride semiconductor can have an energy band gap Eg of about 1.95xcx9c6.0 eV depending on its composition. In this respect, it has received much attention as a material of a semiconductor light-emitting element such as a light-emitting diode and a laser diode.
A general laser diode has a confined structure in which light and carrier are respectively confined. In other words, an InGaN active layer is formed between GaN wave guide layers, and an AlGaN cladding layer is formed around the GaN wave guide layers.
Such a laser diode has a multilayered complex structure, and various variations can be made in its structure to implement an optimal structure for improvement of optical characteristic and thermal characteristic.
However, very high stress occurs between the wave guide layer and the active layer due to the difference of lattice constants between the GaN and AlGaN used as materials of the wave guide layer and the cladding layer and the InGaN used as a material of the active layer. This causes a large quantity of cracks.
In more detail, in fabricating the semiconductor laser diode, if the AlGaN cladding layer and the GaN wave guide layer are directly grown at a high temperature of about 1000xc2x0 C. or greater on the InGaN active layer formed at a low temperature of about 800xc2x0 C. or less, In within the InGaN active layer is evaporated by heat. This could lead to an uneven composition of In within the active layer and a rough interface of the active layer, thereby remarkably deteriorating optical characteristic.
Accordingly, the present invention is directed to a nitride semiconductor light-emitting element and a method for fabricating the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a nitride semiconductor light-emitting element and a method for fabricating the same, in which a rough interface caused by a difference between lattice constants is prevented from occurring.
Another object of the present invention is to provide a nitride semiconductor light-emitting element and a method for fabricating the same, in which low carrier confinement efficiency is improved.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a nitride semiconductor light-emitting element according to the present invention includes a substrate, a first conductivity type cladding layer formed on the substrate, an active layer formed on the first conductivity type cladding layer, a second conductivity type cladding layer formed on the active layer, a buffer layer formed either between the first conductivity type cladding layer and the active layer or between the second conductivity type cladding layer and the active layer, a second conductivity type electrode formed over the second conductivity type cladding layer, and a first conductivity type electrode formed either below the substrate or over the first conductivity type cladding layer.
The buffer layer has a thickness of 0.01xcx9c5 nm, and is formed of one of GaN, AlGaN, and InGaN if the active layer is formed of InGaN.
If the buffer layer is formed of InGaN, a composition of In is smaller than that of In in the active layer.
In another aspect, a method for fabricating a nitride semiconductor light-emitting element according to the present invention includes the steps of sequentially forming a first conductivity type cladding layer, an active layer, a buffer layer, and a second conductivity type cladding layer on a substrate, and forming a second conductivity type electrode over the second conductivity type cladding layer and a first conductivity type electrode either below the substrate or over the first conductivity type cladding layer.
The buffer layer may be formed before the active layer is formed on the first conductivity type cladding layer.
The active layer is grown at a low temperature of 800xc2x0 C. or less, the buffer layer is grown at a low temperature of 900xc2x0 C. or less, and the second conductivity type cladding layer is grown at a high temperature of 1000xc2x0 C. or greater. In this case, loss of the active layer that may occur due to temperature increase is reduced. Thus, interface characteristic between the active layer and the cladding layer formed on the active layer can be improved to facilitate flow of carriers and improve efficiency of carrier confinement, thereby obtaining a nitride semiconductor light-emitting element having high efficiency optical characteristic and thermal characteristic.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.